One of the most commonly employed methods for separating the components of organic liquid mixtures is distillation. However, distillation cannot be conveniently employed when the components which it is desired to separate have boiling points that are close together. For example, when the boiling points of the components of a liquid mixture are very close together, e.g. only a few degrees centigrade apart, it requires a distillation column having an inordinantly high number of trays to effect good separation of the components. Separation of the components of a liquid mixture by distillation is impossible when the components form an azeotrope, i.e., a constant boiling mixture, because the distillate will always contain the components in the same ratio as the boiling mixture. When it is desired to separate two or more components of a liquid mixture which forms an azeotropic combination, means other than simple distillation must be resorted to. One alternate technique for the separation of the components of azeotropic liquid mixtures is solvent extraction. This method can often be used when one of the components is soluble in a third liquid and the other is not. It is often difficult, though, to find a liquid which is a good solvent for one liquid but a poor solvent for the other liquid of a two liquid mixture.
The separation of isopropyl acetate and ethanol from an isopropyl acetate-ethanol-water mixture, which is difficult because this system forms a ternary azeotropic mixture, is further complicated by the fact that isopropyl acetate and water, isopropyl acetate and ethanol and ethanol and water each form binary azeotropic mixtures. Furthermore, these azeotropes have boiling points that are only a few degrees apart. Specifically, the boiling point of the ternary azeotropic mixture is 74.8 degrees C., that of an isopropyl acetate-water azeotropic mixture is 76.6 degrees C., that of an isopropyl acetate-ethanol azeotropic mixture is 76.8 degrees C., and that of an ethanol-water azeotropic mixture is 78.2 degrees C. Thus it is clear that methods other than straight distillation must be used to recover isopropyl acetate and ethanol from this ternary system.
Isopropyl acetate is only slightly soluble in water, thus presenting the possibility of separating the above ternary system by means of extraction. However extraction alone does not generally provide a clean enough separation of the isopropyl acetate and ethanol. The present invention provides a process which permits the recovery of an isopropyl acetate stream which is substantially free of ethanol and an ethanol stream which is substantially free of isopropyl acetate.